TiCl_4改性钠基膨润土的制备及其对U(Ⅵ)和Th(Ⅳ)的吸附性能研究

Preparation of TiCl_4 modified sodium bentonite and its adsorption capacity for U (Ⅵ) and Th (Ⅳ)

采用阳离子插层法制备了TiCl_4改性的钠基膨润土(Ti-Na-bent),并研究了Ti-Na-bent对U(Ⅵ)和Th(Ⅳ)的吸附性能。扫描电镜(SEM)和X射线粉末衍射(XRD)表征结果显示,钛以粒状非晶态的形式存在于钠基膨润土(Na-bent)的表面或层间。吸附实验结果表明,当温度为298K,吸附剂用量为10mg,U(Ⅵ)、Th(Ⅳ)初始质量浓度为500mg/L,pH分别为5.0、2.5,反应时间为2h时,Ti-Na-bent对U(Ⅵ)和Th(Ⅳ)的最大吸附量分别为336.25、231.62mg/g,比改性前分别提高了1.67倍、70%。吸附U(Ⅵ)和Th(Ⅳ)的过程符合Freundlich模型和准二级动力学模型,属于吸热、熵增的自发过程,吸附机理主要为UO_2^(2+)、Th^(4+)、[(UO_2)_n(OH)_(2n-1)]^+、[Th(OH)_2]^(2+)与Na-bent上可交换的阳离子和Ti(OH)_4上的氢之间的离子交换。Ti-Na-bent对U(Ⅵ)、Th(Ⅳ)的吸附容量高、稳定性好,有望用于处理含U(Ⅵ)、Th(Ⅳ)的放射性废水和用作高放废物地质处置库缓冲/回填材料。

TiCl4 modified sodium bentonite(Ti-Na-bent)was prepared by cationic intercalation for efficient adsorption of U(Ⅵ)and Th(Ⅳ).Scanning electron microscopy(SEM)and X-ray powder diffraction(XRD)results showed that titanium existed in the form of granular and amorphous state on the surface or the interlayer of sodium bentonite(Na-bent).Adsorption experiment results showed that at 298 K,the amount of adsorbent was 10 mg,the initial concentration of U(Ⅵ)and Th(Ⅳ)was 500 mg/L,the pH was 5.0,2.5,and the reaction time was 2 h,the maximum adsorption capacity of U(Ⅵ)and Th(Ⅳ)by Ti-Na-bent was 336.25 and 231.62 mg/g,respectively,which was 1.67 times and 70%higher than that before modification.The adsorption process fitted well with the Freundlich model and pseudo-second-order model,it demonstrated that the adsorption was a spontaneous process that was endothermic and entropic.The adsorption mechanism was mainly ion exchange between UO2^2+,Th^4+,[(UO 2)n(OH)n-1]^+,[Th(OH)2]^2+and exchangeable cations on Na-bent and the H on the Ti(OH)4.Ti-Na-bent had high adsorption capacity for U(Ⅵ)and Th(Ⅳ)and good stability,it could be used for the treatment of radioactive waste water containing U(Ⅵ)and Th(Ⅳ),and be used as buffer/backfill material for geological disposal of high level radioactive waste.